The Symphonium Helios is 8.5Ω at 83.3 dB/mW; the Symphonium Meteor is 9.7Ω at 90.9 dB/mW. This page is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.
The Helios needs 7.6 dB more than the Meteor to reach the same loudness — 47 mW against 8.1 mW.
| Specification | Helios | Meteor |
|---|---|---|
| Impedance | 8.5 Ω | 9.7 Ω |
| Sensitivity | 83.3 dB/mW | 90.9 dB/mW |
| Sensitivity (voltage) | 104.0 dB/V | 111.0 dB/V |
| Power for 100 dB | 47 mW | 8.1 mW |
| Voltage for 100 dB | 0.63 V | 0.28 V |
| Current for 100 dB | 74.2 mA | 28.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.06 Ω | 1.21 Ω |
| Sources that reach 100 dB out of 280 | 179 | 271 |
92 of the 280 sources have the power for the Meteor but not for the Helios — Apple USB-C dongle (US), Generic CX31993 dongles, JadeAudio JA11, 89 more.
4 sources are low enough in output impedance for the Meteor under the one-eighth rule but not for the Helios (FiiO K11, FiiO BTR7, FiiO Q7, 1 more).
179 of the 280 sources here reach 100 dB on both. That count is about power only — the output-impedance and hiss lines above are separate questions, and a source can pass this one and fail those.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: Symphonium Helios and Symphonium Meteor. Every figure on this page comes from what Symphonium published, or is derived from it — what that maker publishes, counted.